[Mpiwg-large-counts] Large Count - the principles for counts, sizes, and byte and nonbyte displacements

[Jeff Hammond]

Jim (cc) suffered the most in MPI 3.0 days because of AINT_DIFF and
AINT_SUM, so maybe he wants to create this ticket.

Jeff

On Thu, Oct 24, 2019 at 2:41 PM Jeff Squyres (jsquyres) <jsquyres at cisco.com>
wrote:

> Not opposed to ditching segmented addressing at all.  We'd need a ticket
> for this ASAP, though.
>
> This whole conversation is predicated on:
>
> - MPI supposedly supports segmented addressing
> - MPI_Aint is not sufficient for modern segmented addressing (i.e.,
> representing an address that may not be in main RAM and is not mapped in to
> the current process' linear address space)
>
> If we no longer care about segmented addressing, that makes a whole bunch
> of BigCount stuff a LOT easier.  E.g., MPI_Aint can basically be a
> non-segment-supporting address integer.  AINT_DIFF and AINT_SUM can go
> away, too.
>
>
>
> On Oct 24, 2019, at 5:35 PM, Jeff Hammond via mpiwg-large-counts <
> mpiwg-large-counts at lists.mpi-forum.org> wrote:
>
> Rolf:
>
> Before anybody spends any time analyzing how we handle segmented
> addressing, I want you to provide an example of a platform where this is
> relevant.  What system can you boot today that needs this and what MPI
> libraries have expressed an interest in supporting it?
>
> For anyone who didn't hear, ISO C and C++ have finally committed to
> twos-complement integers (
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0907r1.html,
> http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2218.htm) because modern
> programmers should not be limited by hardware designs from the 1960s.  We
> should similarly not waste our time on obsolete features like segmentation.
>
> Jeff
>
> On Thu, Oct 24, 2019 at 10:13 AM Rolf Rabenseifner via mpiwg-large-counts <
> mpiwg-large-counts at lists.mpi-forum.org> wrote:
>
>> > I think that changes the conversation entirely, right?
>>
>> Not the first part, the state-of-current-MPI.
>>
>> It may change something for the future, or a new interface may be needed.
>>
>> Please, can you describe how MPI_Get_address can work with the
>> different variables from different memory segments.
>>
>> Or whether a completely new function or a set of functions is needed.
>>
>> If we can still express variables from all memory segments as
>> input to MPI_Get_address, there may be still a way to flatten
>> the result of some internal address-iquiry into a flattened
>> signed integer with the same behavior as MPI_Aint today.
>>
>> If this is impossible, then new way of thinking and solution
>> may be needed.
>>
>> I really want to see examples for all current stuff as you
>> mentioned in your last email.
>>
>> Best regards
>> Rolf
>>
>> ----- Original Message -----
>> > From: "Jeff Squyres" <jsquyres at cisco.com>
>> > To: "Rolf Rabenseifner" <rabenseifner at hlrs.de>
>> > Cc: "mpiwg-large-counts" <mpiwg-large-counts at lists.mpi-forum.org>
>> > Sent: Thursday, October 24, 2019 5:27:31 PM
>> > Subject: Re: [Mpiwg-large-counts] Large Count - the principles for
>> counts, sizes, and byte and nonbyte displacements
>>
>> > On Oct 24, 2019, at 11:15 AM, Rolf Rabenseifner
>> > <rabenseifner at hlrs.de<mailto:rabenseifner at hlrs.de>> wrote:
>> >
>> > For me, it looked like that there was some misunderstanding
>> > of the concept that absolute and relative addresses
>> > and number of bytes that can be stored in MPI_Aint.
>> >
>> > ...with the caveat that MPI_Aint -- as it is right now -- does not
>> support
>> > modern segmented memory systems (i.e., where you need more than a small
>> number
>> > of bits to indicate the segment where the memory lives).
>> >
>> > I think that changes the conversation entirely, right?
>> >
>> > --
>> > Jeff Squyres
>> > jsquyres at cisco.com<mailto:jsquyres at cisco.com>
>>
>> --
>> Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de .
>> High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 .
>> University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 .
>> Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner .
>> Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) .
>> _______________________________________________
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>> mpiwg-large-counts at lists.mpi-forum.org
>> https://lists.mpi-forum.org/mailman/listinfo/mpiwg-large-counts
>>
>
>
> --
> Jeff Hammond
> jeff.science at gmail.com
> http://jeffhammond.github.io/
> _______________________________________________
> mpiwg-large-counts mailing list
> mpiwg-large-counts at lists.mpi-forum.org
> https://lists.mpi-forum.org/mailman/listinfo/mpiwg-large-counts
>
>
>
> --
> Jeff Squyres
> jsquyres at cisco.com
>
>

-- 
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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